The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
The present disclosure broadly relates to cement and cementing operations.
Hydraulic cement is any substance provided (at least at one time in the manufacturing process) in a powdered or granular form, that when mixed with a suitable amount of water, can form a paste that can be poured or molded to set as a solid mass. In the oil and gas industry, good bonding between set cement and casing, and also between set cement and the formation, are essential for effective zonal isolation. Poor bonding limits production and reduces the effectiveness of stimulation treatments. Communication between zones can be caused by inadequate mud removal, poor cement/formation bonding, expansion and contraction of the casing resulting from internal pressure variations or thermal stresses, and cement contamination by drilling or formation fluids. Under such circumstances a small gap or microannulus may form at the cement/casing interface, the cement/formation interface, or both.
The addition of charcoal with wood resin-coated aluminum particles for an expansive cement is disclosed in U.S. Pat. Nos. 4,332,619 and 4,328,038. The use of encapsulated gas and other expanding fluids is disclosed in U.S. Pat. Nos. 7,494,544 and 7,156,174.
Portland cement manufacturers have employed shrinkage-compensating cements that include an offsetting “expansive cement”, which is a hydraulic cement that, after setting, increases in volume to significantly greater degree than Portland cement paste to form an expanded set cement as defined in the American Concrete Institute 223R-10 Guide for the Use of Shrinkage-Compensating Concrete (2010). Representative examples of shrinkage-compensating cement are found in U.S. Pat. No. 7,988,782, US20150107493 and U.S. Pat. No. 4,419,136.
Expansive cement has also been used in the oil and gas industry to cement wells. Representative examples of this technology are found in U.S. Pat. Nos. 2,465,278, 3,884,710, 4,002,483, 4,797,159, 5,942,031, 6,966,376, and U.S. Ser. No. 14/307,430. Use of expanding agents to cement wells is problematic since the expanding agents known in the art begin hydrating and thus begin to expand as soon as they contact water. Accordingly, if the expanding agent is going to expand the cement after the cement slurry is positioned within the well, the expanding agent cannot be added to the cement slurry mix water. Also, when the expansion agent is added to the slurry, the viscosity and/or yield stress of the slurry increase before the slurry can be placed and set. This is especially problematic when the cement slurry is exposed to increased temperature conditions such as are frequently encountered downhole in a well. Incorporation of expanding agents thus leads to difficulties in pumping and placement of the slurry, along with complicating job design.
Moreover, since the cement slurry is readily flowable, any hydration of the expanding agent that occurs before the cement begins to set does not contribute to producing a compressive force within the annulus of the well due to the expansion of the set cement.
Various efforts to delay expansion have been suggested. Coating of metal oxide particles with non-hydratable or previously hydrated minerals such as metal carbonates, hydroxides and hydrates was suggested in U.S. Pat. Nos. 4,332,619, 5,741,357, EP2169027A1; but these materials can be difficult to prepare and have had only limited success.
The cement industry in general, is in need of ways to improve the preparation, handling and design of hydraulic cements with hydratable expanding agents that address these problems and shortcomings; and the oil and gas industry is in need of ways to better and more controllably delay expansion of the expanding agents, and to improve the bonding between the set cement and the casing within the well annulus.